Interior Minister Jesse Chacon said C-4 explosives were used to blow up the pipeline Saturday night and that officials believed the act was aimed at trying to destabilize the country.
"We already know who is behind this situation, and we have made some arrests," Chacon said, without giving details.
Nobody was hurt by the explosion Saturday night in a remote region of western Venezuela, and firefighters quickly extinguished a fierce blaze caused by the blast.
Oil Minister Rafael Ramirez blamed the same opponents who unsuccessfully tried to oust President Hugo Chavez in a two-month strike that ended in early 2003.
"The same people behind the oil sabotage ... are trying to wreak havoc in our country," Ramirez told the government-run Bolivarian News Agency. "We defeated them that time, and we will defeat them now."
The state oil company said the pipeline, which includes two pipes, carries 400,000 barrels of crude a day to the giant Amuay refinery. Firefighters said only one of the two pipes was broken open. Residents in the area heard two blasts, firefighters said.
The refinery has enough inventories to cover supply needs while the pipeline undergoes repairs, which should take at least five days, Ramirez said.
Vice President Jose Vicente Rangel called the pipeline blast a "criminal, unacceptable act." He indicated former oil workers could have been involved.
The military said it was stepping up security at key oil installations to prevent any other acts of sabotage in the country, the world's fifth largest oil exporter.
Ramirez said the state oil firm Petroleos de Venezuela S.A., or PDVSA, had been the "target" of a campaign to try to destabilize the country. He showed reporters images of flames leaping from the pipeline after the blast.
Chacon said the act didn't get in the way of the vote. "Venezuelans said 'no' to violence today," he said.
Government officials said 11 people suspected of plotting to use violence to interrupt balloting were arrested in Zulia state while a large cache of weapons, including C-4 explosives and grenades, was seized in central Guarico state.
Officials in Caracas also reported blasts from small explosives that reportedly injured three people on Friday.